FIG. 9 shows a conventional component placement machine generally indicated by reference numeral 10 for mounting electronic components on a circuit substrate. The component placement machine 10 has a component supply 11 for supplying electronic components 12, a placement head 13 for picking up components 12 from the component supply 11 and then placing the components 12 onto a circuit substrate 14, a transport device 15 for transporting the placement head 13 from one place to another, a recognition device 16 or a camera for recognizing positions, i.e., horizontal and angular positions, of the component 12 held by the placement head 13, a substrate holder 17 for supplying the circuit substrate 14 into the component placement machine 10 and then hold it in the machine, and a controller 18 for controlling overall operations of the component placement machine 10.
The component supply 11 holds one or more component supply cassettes 19. Each component supply cassette 19 supports a component supply reel 20 around which a tape carrying electronic components is wound. The placement head 13 has a vacuum quill 21 for sucking and thereby holding the component 12. The quill 21 is mechanically connected with an angular control mechanism 22 so that it can rotate about a vertical axis parallel to Z-axis indicated in the drawing to make an angular adjustment of the component held thereon. The transport device 15 has an X-axis transport mechanism 23 and Y-axis transport mechanism 24 for a horizontal movement of the placement head 13. The circuit substrate 14 may be a substrate on which one or more electronic components have already been mounted before being supplied into the placement machine. In this instance, additional electronic components 12 may be mounted on that particular circuit substrate. The recognition device 16 for recognizing the component 12 held by the quill 21 is electrically connected to an image processor 25 where an image picked up by the recognition device 16 is used for a determination whether the component is properly held on the quill or not.
In operation of the component placement machine 10 so constructed, the components 12 to be mounted are supplied to a component supply station (not shown in the drawing)n by means of the component supply cassette 19 held by the component supply 11. The placement head 13 arrives above the component supply, and then the quill 21 moves down toward the component 12 and suck it. Then, the quill 21 moves up together with the component 12 held thereto. Subsequently, the placement head 13 is transported by the transport device 15 to a position opposing the recognition device 16. The recognition device 16 catches an image of the component 12 held by the quill 21. The image is then transmitted to the image processor 25. The image processor 25 performs a certain image process to determine possible horizontal and/or angular misalignment of the component 12, which is then transmitted to the controller 18. Using the determined misalignment, the controller 18 adjusts the position of the placement head 13 that is moving toward the circuit substrate 14, so that the component 12 is correctly positioned above the circuit substrate 14. The component 12 is then mounted onto the substrate 14 by the downward movement of the quill 21.
FIGS. 10 and 11 show the component supply cassette 19 and the reel 20 attached thereto. As best seen in FIG. 11, a number of components 12 are carried by a component carrier 26 in the form of a strip or a tape by having regular intervals 27 among each other. More specifically, the component carrier 26 has a base tape 28 having relatively large thickness. The base tape 28 has a number of cavities 29 or concave portions formed on one surface thereof at the regular intervals 27 so that in each of the cavities 29 a corresponding electronic component 12 is contained. To prevent the component 12 from dropping out of the cavity 29 and/or blocking invasion of dust into the cavity 29, one surface of the base tape 28 is covered with a thin top tape 30 in the form of a strip attached thereto. In operation of the component supply 11, a portion of the top tape 30 is peeled off immediately before reaching the component pickup station, thereby allowing the quill 21 to access the component 12 contained inside the cavity. The base tape 28 also has a number of perforations 31 formed therein at regular intervals.
As shown in FIG. 12, the component supply cassette 19 has a main frame 32 for defining a transport passage 33 of the component carrier, indicated by a dotted line. The main frame 32 carries a support shaft 34 on which the component supply reel 20 is detachably mounted, a shutter mechanism 35 for peeling off the top tape from the base tape and then exposing the component to the quill at the pickup station for the pickup operation of the component, a feed mechanism 36 for feeding the component carrier intermittently, a reel drive mechanism 38 for rotating a winding reel 37, and a tape guide member 39 for guiding the base tape after it has been separated from the top tape.
As shown in FIGS. 13A-13C and 14A-14D, the shutter mechanism 35 has a fixed guide 40 along and under which the component carrier 26 is transported. The fixed guide 40 has an upstream guide plate 41 and a downstream guide plates 42 positioned on upstream side and downstream side, respectively, of a direction indicated by an arrow 43, along which the component carrier is transported, and thereby defining an opening 44 between these two guide plates 41 and 42. A movable guide plate or a shutter 45 in the form of plate is positioned between the upstream and downstream guide plates 41 and 42. The shutter 45 is arranged to move back and forth in the carrier transporting direction 43 between a first position adjacent to the upstream guide plate 41 where it opens the component pickup station 46 for allowing the quill to access the component, and a second position adjacent to the downstream guide plate 42 where it closes the component pickup station 46, preventing the quill to access the component. For this purpose, the shutter 45 is drivingly connected with the feed mechanism 36, which will be described below. The movable shutter 45 has a slot 70 extending in a transverse direction through which the peeled top tape is pulled out toward the winding reel 37.
As shown in FIG. 15, the reel drive mechanism 38 of the component supply cassette has a support shaft 47 around which the winding reel 37 is supported for rotation. The shaft 47 is connected with an operation lever 48 and a winding lever 49. In turn, the operation lever 48 is connected with one end of a linkage 50 for moving the shutter 45, and the winding lever 49 is connected at its free end with a biasing spring 51 so that the levers 48 and 49 are biased in a direction indicated by an arrow 52 (i.e., counterclockwise direction in the drawing). A one-way clutch 53 is disposed between the support shaft 47 and the winding reel 37 so that the winding reel 37 follows rotation of the levers 48 and 49 in the clockwise direction in the drawing but it does not follow rotation of these levers in the counterclockwise direction. That is, when the operation lever 48 is rotated in the clockwise direction against the biasing spring 51, the winding reel 37 rotates in the same direction for winding a certain length of the peeled top tape, and when the operation lever 48 is rotated by the biasing spring 51 in the counterclockwise direction, the winding reel 37 stays without any rotation.
As shown in FIG. 16, the feed mechanism 36 of the component supply cassette for intermittent transportation of the component carrier includes a shaft 52 around which a wheel lever 53 is rotatably secured. The wheel lever 53 is connected to the other end of the linkage 50 (see FIG. 15) through a pivot 54 so that the linkage 50 may rotate about the pivot 54 freely. The wheel lever 53 has an actuator 55 or lever defined therein, which engages with the shutter 45. Specifically, the shutter 45 has a side plate 56 defined with a U-shaped cutout 47 with which the actuator 55 engages. This allows that rotation of the wheel lever 53 causes the shutter 45 to move back and forth in the carrier transporting direction 43.
For the purpose of intermittent feeding of the base tape, a feed wheel 58 and a ratchet wheel 59 secured to the feed wheel 58 by bolts 60 are supported for rotation about the shaft 52 through a one-way clutch 61. The one-way clutch 61 functions so that the feed and ratchet wheels 58 and 59 follow rotation of the wheel lever 53 in the counterclockwise direction 62 in the drawing but they do not follow the rotation of the wheel lever 53 in the clockwise direction 63. The ratchet wheel 59 is provided at its periphery with a number of teeth 64.
A ratchet lever 65 is rotatably secured to the wheel lever 53 and it engages with ratchet teeth 64 of the ratchet wheel 59. A stop lever 66 is rotatably secured to the frame of the cassette and it also engages with ratchet teeth 64 of the ratchet wheel 59 so as to prevent free rotation of the wheels 58 and 59 in the clockwise direction but it allows rotation of these wheels in the counterclockwise direction in the drawing. In order to feed the base tape 28 in synchronism with rotation of the wheel 58, the feed wheel 58 is provided at its periphery with a number of teeth 67 for engagement with the perforations 31 formed in the base tape 28.
In operation, the operation lever 48 is rotated in the clockwise direction in FIG. 15. Upon this rotation, the winding reel 37 is rotated in the same direction and wind up peeled top tape. At the same time, a certain length of the top tape located near the slot 70 of the shutter is peeled off from the base tape. Rotation of the operation lever 48 also rotates the wheel lever 53 in the direction 63 shown in FIG. 16, and this causes movement of the shutter 45 against the component carrier transporting direction 43. As a result, the component 12 is exposed to the quill 21 at the pickup station 46. With the rotation of the wheel lever 53 in the direction shown by the arrow 63, the ratchet lever 65 slides over several teeth 64 of the ratchet wheel 59. Throughout this rotation, the stop lever 66 continues to engage with one specific tooth 64 of the ratchet wheel 59, so that the ratchet wheel 59 as well as the feed wheel 58 stays without rotation.
Then, when the operation lever 48 is released, the lever 48 rotates in the counterclockwise direction by the biasing force of the spring 51, as shown in FIG. 15. By this rotation of the operation lever 48, the linkage 50 rotates the wheel lever 53 in the counterclockwise direction in FIG. 16. As shown in FIG. 16, with this rotation of the wheel lever 53, the ratchet lever 65 engaged with a certain tooth 64 of the ratchet wheel 59 causes the ratchet wheel 59 as well as the feed wheel 58 to rotate in the counterclockwise direction. At this moment, the stop lever 66 slides over the ratchet teeth 64 so as to allow rotation of the ratchet wheel 59 relative to the stop lever 66. Also, by rotation of the actuator 55, the shutter is moved in the direction shown by the arrow 43 to close the component pickup station 46.
With the rotation of the feed wheel 58 in the counterclockwise direction, the base tape 28 is forwarded by a certain distance in the direction 43 due to engagement of its perforations 31 with the tooth 67. This causes the subsequent cavity 29 and the component 12 contained therein to be moved to the component pickup station 46. By repetition of the above-described operations, the components 12 carried by the component carrier 26 are picked up by the quill 21 one after another intermittently, and then mounted on the circuit substrate.
The size of electronic components supplied by tapes or component carriers varies in a wide range. For example, a relatively small component has a size of 1.0 mm×0.5 mm×0.5 mm or even 0.6 mm×0.3 mm×0.3 mm. Generally, each component is contained inside the cavity of the component carrier in a most stable condition, i.e., with its major surface faces vertically. Although, in case of a particularly small and lightweight component, it is likely to bounce up and around inside the cavity because of vibrations transmitted not only from driving mechanism included in the component supply cassette itself but also from others included in devices located nearby.
Therefore, after the top tape is peeled off from the base tape, if nothing exists in place of the top tape, it may happen that the component takes an upright position with its major surface faces horizontally. This is so problematic because the component in such an upright position prevents its correct mounting onto the circuit substrate as well as its vacuum sucking by the quill.
In order to solve this problem, a variety of techniques related to the mechanisms to be employed around the component pickup station have been developed. In one example, as shown in FIGS. 13A to 13C, upper side guide member of the component supply cassette is separated into two guide plates 41 and 42. The shutter 45 is then provided between these two guide plates 41 and 42 so that the shutter 45 may move between the first position adjacent to the upstream guide plate 41, and the second position adjacent to the downstream guide plate 42.
With this arrangement, as shown in FIG. 13A, when the shutter 45 takes the first position, the electronic component (not shown in the drawing) is exposed between the shutter 45 and the downstream guide plate 42, thereby the component may be picked up by the quill. After the pickup operation of the component, as shown in FIG. 13B, the shutter 45 moves to the second position adjacent to the downstream guide plate 42. At the same time, the component carrier 26 is forwarded by a predetermined distance, so that the subsequent component 12 is transported to the pickup station 46. At this moment, as can be seen from the drawing, the component to be picked up is still covered by the shutter 45. This prevents the component from taking the upright position. Next, as shown in FIG. 13C, the shutter 45 moves backward to the first position adjacent to the upstream guide plate 41. This allows the component 12 to be picked up by the quill.
During such an operation, as shown in FIGS. 14A to 14D, the top tape 30 is peeled off from the base tape 28 at the movement of the shutter 45 from the second position to the first position in synchronism with the rotation of the winding reel. Disadvantageously, after this backward movement of the shutter 45 uncovering the base tape results in that revealed portion of the base tape 28 is subject to vibrations, which causes the component 12 to bounce up and around inside the cavity 29. Eventually, this may cause difficulties in the subsequent vacuum sucking operation by the quill.
In addition, especially for the case of a relatively vulnerable base tape, e.g., the base tape for chip components having a size of 0.6 mm×0.3 mm (so called 0603 chips), as shown in FIG. 14D, the movement of the shutter 45 from its first position to the second position may drag the revealed part of such base tape 28 and nip it with the second guide plate 42, which results in the transport defect of the component carrier 26.
Besides, a variety of research studies revealed that deformation of a portion of the base tape adjacent to the downstream guide plate where the base tape is disengaged from the feed wheel transmits vibration to the component in the pickup station. More specifically, as shown in FIG. 17, in the conventional component supply cassette, the downstream guide plate 42 is designed to provide a minimum frictional force to the disengaging base tape 28. Also, a third guide plate 71 is positioned on the downward side of the downstream guide plate 42 for directing the disengaged base tape 28 downward so that it defines a relatively large space 72 with respect to the feed wheel 58. This causes the disengaged base tape 28 to travel in a direction substantially parallel to the tangential line of the wheel 58. However, the disengaged and curved tape 28 encourages vibration which is then transmitted to the other portion of the base tape 28 located in the pickup station, causing the component to bounce up and take an upright position inside the cavity.
Also, another technique has been disclosed in Japanese patent publication 9-186487 (A) for preventing the bouncing of the component. Specifically, as shown in FIG. 18, a permanent magnet 75 is disposed under the tape transport passage in a region of the tape peeling station and the component pickup station. The permanent magnet 75 attracts the components positioned in this area, where the top tape for covering such components has been peeled off, so as to retain these components in their proper position inside the corresponding cavities. This arrangement may effectively prevent the component from bouncing up or dropping out of the cavity caused by vibrations as well as an electrostatic force generated as a result of peeling off of the top tape.
In the meantime, electronic components to be mounted on the circuit substrate typically use magnetic materials for their electrodes, which makes the electronic components to be attracted by the magnet. However, if the electrodes are plated with palladium, or the component itself is in a very small size, the magnetic force attracting such a component is considerably weak. Even such small components, however, may be attracted by enhancing the magnetic field of the magnet as much as, for example, 100 Gausses or above.
In order to facilitate pickup operation by the quill 21 even with the existence of such magnetic attraction force, a thrust pin 76 may be disposed under the pickup station 46 as indicated by the dotted line in the drawing. The thrust pin 76 is mechanically connected with the operation lever 48 so that, when the lever 48 is rotated in the clockwise direction in the drawing, the thrust pin is driven to move upward. As shown in FIG. 19, in order to allow the thrust pin 76 to contact a bottom surface of the component 12 and lift it up, there is formed a through-hole 77 in a corresponding portion of the magnet 75.
Although the thrust pin 76 effectively helps the vacuum quill 21 for picking up the component 12, this arrangement tends to increase the vacuum force F2 (see FIG. 20) needed for the quill 21 to pick up the component 12. This means that an excessive attraction force F1 (see FIG. 20) by the magnet 75 will make it difficult for the vacuum quill 21 to pick up the component 12, which in turn limits the attraction force by the magnet 75. Also, the magnetic field generated around the pickup station 46 may cause an adverse affect on positioning the component 12 held by the quill 21 in a proper condition.
In addition, due to bouncing of the component inside the cavity may dislocate a contact position between the component and the thrust pin. In this instance, the larger component may be held properly by the quill in a correct position, whereas the smaller component may be held by the quill in an incorrect position.